Cataract surgery has been performed for many years. Toric intraocular lenses have been available for many years (StarSurgical/Rayner) but recently Alcon has popularised their use. This lens is particularly useful for patients having astigmatism. Roughly one third of all patients requiring cataract surgery have astigmatism and in order for the intraocular lens to function correctly it must be accurately placed. It is estimated that for every degree of incorrect orientation, the astigmic correction factor for such an intraocular lens decreases by approximately 3%. As a consequence, pre-operative marking is imperative for accurate surgery.
However, measurements on the patient's eye which are conducted pre-operatively are conducted in the consulting rooms of the ophthalmic surgeon where the patient sits upright with his torso in a vertical position. However, when the patient lies down, and is thus supine as required for surgery, the eye rotates by a variable amount which differs considerably from patient to patient. Thus the intention of the marking procedure is to enable the eye to be marked with reference markings which can be used to determine the correct alignment of the intraocular lens, the correct alignment of incisions, etc., during surgery. The marks themselves are made with a dye that is painted onto or otherwise applied to various prongs of the marker and which are accurately pressed onto the eye whilst the patient is seated and thus has his head vertical.
There are three basic prior art marking devices. One class of such devices are free hand systems where the marking prongs are located at one end of an elongate stem or pencil like handle which is held by the ophthalmic surgeon. This relies upon the dexterity of the surgeon. There is another device which incorporates a small spirit level into the handle in order to indicate a horizontal plane. There is a third class of markers which incorporate a plumb bob and thus rely upon gravitational forces to maintain the marking device aligned with the vertical. It is with this class of marking devices that the present invention is concerned. The particular prior art device which gave rise to the present invention is manufactured by Rumex of St Petersburg, Fla., USA.